1. Field of the Invention
The present invention relates to an organic bistable element, which can be operated at a low drive voltage and in which the degree of a difference in threshold voltage between information writing and information reading can be regulated by regulating the thickness of members constituting the element, a memory device using the same, and a method for driving the organic bistable element and the memory device.
2. Background Art
A conventional organic bistable element has a laminate structure in which a ferroelectric layer is interposed between a pair of electrodes. For example, anthracene and TTF-CA (an alternately laminated charge transfer complex of tetrathiafulvalene and tetrachloro-p-benzoquinone) have been studied for use as compounds for constituting the ferroelectric layer (see, for example, Japanese Patent Laid-Open No. 345431/2001 on pages 2 and 3, FIG. 1).
Further, an organic bistable element has also been proposed in which a laminate having a three-layer structure comprising an electrically conductive thin film interposed between two layers of low-electrically conductive organic thin film having a two-layer structure is used instead of the ferroelectric layer and is interposed between a pair of electrodes. In this case, AIDCN (2-amino-4,5-dicyanoimidazole) is used as the material for constituting the low-electrically conductive organic thin film (see, for example, pamphlet of WO 02/37500 on pages 6 to 8, FIG. 2).
The organic bistable element disclosed in Japanese Patent Laid-Open No. 345431/2001 suffers from a problem that, due to a relatively high switching voltage, power consumption in driving is increased. On the other hand, the organic bistable element disclosed in the pamphlet of WO 02/37500 is advantageous in that, as compared with the construction in which only the ferroelectric layer is interposed between the electrodes, the switching voltage can be reduced. Since, however, the drive voltage of the element depends upon compounds constituting the organic thin films, a power source should be newly provided for each compound, or the output voltage should be regulated using a variable power source.
Further, in an actual organic bistable element, providing a suitable level of difference in threshold voltage between information writing and information reading is preferred. In the prior art technique, however, the difference level of threshold voltage between information writing and information reading could not have been regulated.